Process for preparing neutral and functional perfluoropolyethers with controlled molecular weight

ABSTRACT

A process for decomposing perfluoropolyethers to products with a controlled molecular weight, comprising heating the perfluoropolyethers at temperatures of from 150 DEG  to 380 DEG  C. with 0.1%-2% by weight of a catalyst comprising a fluoride and/or oxyfluoride of Al, Ti, V, Co or Ni; and in case to fluorination at high temperatures to obtain completely neutral perfluoropolyethers.

BACKGROUND OF THE INVENTION

It is known to prepare polyperoxy perfluoropolyethers by photochemicaloxidation of fluorolefins as it is described in particular in BritishPat. No. 1,104,482.

It is also known to prepare perfluoropolyethers stable at hightemperatures, obtained from the above polyperoxy perfluoropolyethers byheating them or by using suitable reducing compounds as it is describedin particular in British Pat. No. 1,226,566.

By using perfluoropropene as starting compound, in the processesdescribed in the two above patents, compounds of general formula:##STR1## are obtained, wherein A is --CF₃, --C₂ F₅, --C₃ F₇ and Z is anacid group ##STR2## or a derivative thereof or a group --CO--CF₃.

The monomeric units with indexes m, n and r are randomly distributedalong the chain of the perfluoropolyether; m, n and r are integers from0 to 200, their values depending on the photo-oxidation reactionconditions, and the value of m+n+r being always greater than zero.

By using tetrafluoroethylene as starting compound perfluoropolyethers ofgeneral formula:

    B--O(--CF.sub.2 CF.sub.2 --O).sub.p --(CF.sub.2).sub.q --Z (II)

are obtained, wherein B is --CF₃, --C₂ F₅ and Z is an acid group##STR3## or a derivative thereof; the monomeric units with indexes p andq are randomly distributed along the chain of the perfluoropolyether; pand q are integers and p/q is comprised between 0.5 and 2 (extremesincluded), and their values depend on the photo-oxidation reactionconditions.

There are also known perfluoropolyethers obtained by polymerization inthe presence of anionic catalysts of perfluoropropene epoxide, as it isdescribed for example in U.S. Pat. No. 3,250,808, having generalformula: ##STR4## wherein Y is an acyl fluoride group ##STR5## and m isan integer greater than zero.

The perfluoropolyethers of the three classes above can be subjected toknown treatments in order to obtain neutral perfluoropolyethers. Anexample of the above treatments consists in heating theperfluoropolyether at temperatures of from 100° to 200° C. in thepresence of fluorine.

The general formulae of the perfluoropolyethers obtained are: ##STR6##in which A and A', equal or different, can be --CF₃, --C₂ F₅ or --C₃ F₇; m, n, and r have the meaning indicated above;

    B--O--(CF.sub.2 CF.sub.2 O).sub.p --(CF.sub.2 O).sub.q --B'(V)

in which B and B', equal or different, are --CF₃ or --C₂ F₅ ; p and qhave the meaning already indicated;

    C.sub.3 F.sub.7 --O--(C.sub.3 F.sub.6 O).sub.m --R.sub.f   (VI)

in which R_(f) is --C₂ F₅ or --C₃ F₇ ; m is an integer greater thanzero.

THE PRESENT INVENTION

An object of the present invention is a process for decomposingperfluoropolyethers having generale formulae IV, V, VI comprisingheating at temperatures ranging from 150° to 380° C. in the presence ofa catalyst comprising fluorides and/or oxyfluorides of Al or Ti, or V orCo or Ni, or mixtures of the same, in amounts corresponding to 0.1% to2% by weight on the perfluoropolyethers.

Applicants have surprisingly found that, in the presence of an abovecatalyst, the perfluoropolyether chain, independently from thedistribution of the monomeric units present in the chain, is decomposedto form shorter perfluoropolyether chains having terminal groups:##STR7## in which X=F, --CF₃, --CF₂ --CF₃.

Thus, it is possible to obtain the decomposition of theperfluoropolyether chain with formation of perfluoropolyethers having alower number of monomeric units by suitably modifying the reactionconditions, as temperature, reaction time, concentration and type ofcatalyst utilized.

It is also possible to use as starting perfluoropolyether a compound ofthe classes I, II and III. In this case however it is necessary to use agreater amount of catalyst, and greater temperatures and times of thedecomposition treatment, but always in the ranges above indicated.

By selecting the operative conditions above and the characteristics ofthe catalyst employed it is possible, therefore, to obtainperfluoropolyethers having prevailingly the average molecular weightdesired, starting from perfluoropolyethers having a higher molecularweight.

A further advantage obtainable by the process of the present inventionresides in that it is possible to modify the molecular weightdistribution of the perfluoropolyether deriving from an usualperfluoropolyether preparation by increasing the most useful fractions.An important flexibility degree is therefore obtained with the processof the present invention for preparing products having a determinedmolecular weight, from which, as is known, depend the viscosity andvapor pressure of the products.

The conditions for achieving the object of the invention are:

(a) maintaining the temperature in the range of from 150° to 380° C.;

(b) amount and type of the catalyst utilized.

The catalyst amount to be used ranges from 0.1% to 2% by weight referredto the perfluoropolyether, depending on the catalytic activity.

Suitable catalysts for the process according to the invention can alsobe obtained by starting from any compound of the above defined elements,different from fluorides and oxyfluorides, provided that, in thereaction conditions, such compounds be capable of forming, at least inpart, the corresponding fluorides or oxyfluorides, for the releasing offluorine from the perfluoropolyether to be treated.

In the case of cobalt and nickel the Applicant has found that veryefficient catalysts are represented by the trifluorides. Good resultsare obtained also by using other halides of Ni and/or Co, provided thata flow of gaseous fluorine is used, the fluorine providing the formation"in situ" of the trifluoride.

A titanium compound preferably used is TiOF₂.

A catalyst particularly suitable for the process according to theinvention is represented by aluminum fluoride having specific structureand morphologic characteristics.

Allotropic structures in which AlF₃ is present are known, as well as themethods of obtaining the same, in particular reference will be madehereinafter to alpha, beta, gamma and delta structures, characterized bythe X-ray powder diffraction spectrum reported in the technicalliterature (Joint Committee Powder Diffraction Standards 1981 and FrenchPat. No. 1,383,927-Du Pont).

A further important characteristic, which is indicative of the catalyticactivity degree, is the free acidity value determined as irreversiblyfixed ammonia. The determination is carried out as follows: the sampleof AlF₃ is dried at 100° C. for 2 hours, it is weighed (about 1 g) andintroduced into a container, then gases are removed under vacuum(residual pressure below 10⁻⁵ Torr) at 100° C. during 3 hours. The NH₃isothermic absorption is then determined at 100° C. and at a pressurefrom 50 to 400 Torr. The volume of NH₃ absorbed (Vass.) linearly dependson the pressure (P) according to the equation:

    Vass.=A·P+B

The value of B (intercept for P=O) is assumed as "total absorbed NH₃ at100° C.".

Then it is degased for 1 hour at 100° C. under vacuum (residual pressurebelow 10⁻⁵ Torr). The NH₃ isothermic absorption is determined again at100° C. and in a pressure range of from 50 to 400 Torr. The NH₃ absorbedvolume (Vass.) is expressed by the equation:

    Vass.=A'·P+B'

wherein A"=A.

The value B-B' is assumed as "irreversibly NH₃ absorbed at 100° C.".

The values determined for the AlF₃ utilized as catalysts in the examplesare indicated hereinbelow:

    ______________________________________                                        catalyst type:                                                                             I       II      III   IV    V                                    ______________________________________                                        crystalline                                                                            about   85%     70%   60%   --    --                                 phase γ.sub.c :                                                         crystalline                                                                            about   15%     30%   40%   --    --                                 phase δ.sub.c :                                                         crystalline      traces  traces                                                                              traces                                                                              --    --                                 phase β.sub.c :                                                          crystalline      --      --    --    100%  --                                 phase α:                                                                crystalline      --      --    --    --    100%                               phase γ.sub.s :                                                         Specific         16.8    15.4  13.6  6.4   14                                 surface                                                                       (m.sup.2 /g):                                                                 Irreversibly     9.2     8.8   5.9   2.9   7.5                                NH.sub.3 absorb-                                                              ed at 100° C.,                                                         in micro                                                                      eq./g.:                                                                       ______________________________________                                    

γ_(c), δ_(c) and β_(c) phases described above are in particular reportedin French Pat. No. 1,383,927 by J. Christoph and J. Teufer.

γ_(s) phase is described by Crocket and Maenpler in Inorg. Chem. 5 No.11, pages 1927-33 (1966); α-phase is described in Anal. Chem. 29, 984(1957).

AlF₃ phases having the most valuable catalytic properties in the processaccording to the present invention are crystalline gamma and/or deltaform, having a free acidity corresponding to an irreversible NH₃absorption equal to at least 2.9 micro eq/g.

The product obtained according to the process of the present inventionprevailingly consists (up to 95% by weight) of perfluoropolyethershaving neutral terminals.

Said perfluoropolyether can be subjected to fluorination at temperaturesranging from 120° to 250° C. in order to obtain completely neutralperfluoropolyether, having formalae: ##STR8## in which A and A' equal ordifferent, can be --CF₃, --C₂ F₅ or --C₃ F₇ ; m, n, and r have themeaning indicated above;

    B--O--(CF.sub.2 CF.sub.2 O).sub.p --(CF.sub.2 O).sub.q --B'(V)

in which B and B', equal or different, are --CF₃ or --C₂ F₅ ; p and qhave the meaning already indicated;

    C.sub.3 F.sub.7 --O--(C.sub.3 F.sub.6 O).sub.m --R.sub.f   (VI)

in which R_(f) is --C₂ F₅ or --C₃ F₇ ; m is an integer greater thanzero.

The AlF₃ catalyst can also be prepared in situ during the reaction byadding anhydrous AlBr₃ to the starting perfluoropolyether. In fact,under the reaction conditions it is possible to have bromine substitutedby the fluorine released by the perfluoropolyether.

The following examples are given only for illustrative purposes and arenot to be considered however as limiting the present invention. Theviscosity has been determined at 20° C.

EXAMPLE 1

500 g of perfluoropolyether (PFPE) from C₃ F₆ (formula IV) having aviscosity of 1382 c.St. were additioned with 5 g of AlF₃ of type I.After 15-minute reaction at a temperature of 303° C. there werecollected, after filtration of AlF₃, of 375 g of oil having a viscosityequal to 40 c.St. (corresponding to an average molecular weight of 1500a.m.u.) and an acidity equal to 0.2 m.eq.KOH/g. In the dry ice trap, inwhich the volatile reaction products had been collected, 50 g of PFPEexhibiting a viscosity of 4 c.St. and an average molecular weight of 640a.m.u. and a acidity equal to 0.4 m.eq.KOH/g (milliequivalents) wererecovered.

Distillation under vacuum with rectification of the acid product at 40c.St., yielded 150 g of heat products having a viscosity of 8 c.St.,which introduced into a cylindrical photochemical reactor of 150 mlvolume, were irradiated for 18 hours by means of a Hanau lamp TQ 150which emitted in the area 250-300 millimicron a flux of 1.5.10⁻³Einstein/minute.

After such irradiation period, 145 g of an oil having a viscosity of 12c.St. and an acidity of 0.01 m.eq.KOH/g were obtained.

The complete neutralization occurred with KOH at 220° C. in an autoclaveaccording to what is described in British Pat. No. 1,104,482: 135 g of aneutral oil having a viscosity of 15 c.St. were obtained.

EXAMPLE 2

500 g of a PFPE from C₃ F₆ (formula IV) having an average molecularweight equal to 6500 a.m.u. and a viscosity of about 1400 c.St. wereheated in a flask, equipped with a refrigerator, a solid CO₂ trap and astirrer, up to a temperature of 150° C. and then 10 g of AlF₃ (2% byweight) of type II, obtained by treating type I at 520° C. for 3 hours,were added.

The reactor temperature was then brought to 280° C. during 30 minutesand maintained at such temperature for further 30 minutes. At the end ofthe test and after filtration, 453 g of oil with a numeral averagemolecular weight, of 1770 a.m.u., a viscosity of 58 c.St. and an acidityequal to 0.3 m.eq.KOH/g were obtained, while in the CO₂ trap there wererecovered 22 g of a PFPE having an average molecular weight of 850a.m.u. and an acidity equal to 0.5 m.eq.KOH/g of oil.

The fluorination of the product having a molecular weight of 1770 a.m.u.was carried out by bubbling a fluorine flow of 10 l/h for 8 hours at atemperature of 130° C., and gave 445 g of a neutral PFPE having aviscosity of 90 c.St.

A first portion of 220 g was distilled under vacuum rectification, toobtain a neutral PFPE having a viscosity of 61 c.St. 60 g of saidperfluoropolyether were obtained having a vapor pressure, at 20° C. of2×10⁻⁷ Torr.

A second portion of 220 g was distilled under vacuum with rectificationto obtain a neutral PFPE having a viscosity of 147 c.St. 92 g of saidPFPE having a vapor pressure, at 20° C., of 4×10⁻⁸ Torr were obtained.

In such case, 54 g of an undistilled residue having a viscosity of 750c.St. were collected.

EXAMPLE 3

Example 2 was repeated but using the same catalyst type in amounts equalto 1% by weight referred to PFPE, and a reaction time of 60 minutes andat a temperature of 300° C. There were obtained, after filtration, 475 gof an oil having a viscosity of 175 c.St., an average molecular weightof 2850 a.m.u. and an acidity of 0.15 m.eq.KOH/g of oil.

In the dry ice trap, 7 g of a product having a viscosity of 2 c.St. andan average molecular weight of 650 a.m.u. were collected.

The product above, after neutralization by treatment with fluorine,yielded 467 g of neutral oil having a viscosity of 195 c.St. and anaverage molecular weight equal to 2910 a.m.u. A portion of 230 g wasdistilled under vacuum with rectification, to obtain a neutral oilhaving a viscosity equal to 60.5 c.St. 48 g of PFPE having a vaporpressure (20° C.) of 3×10⁻⁷ Torr, were obtained. A second portion of 236g was distilled to obtain a product having a viscosity of 140 c.St. 113g of said PFPE having a vapor pressure (20° C.) of 8×10⁻⁹ Torr and 104 gof an undistillable residue having a viscosity of 755 c.St. and anaverage molecular weight of 5050 a.m.u. were obtained.

EXAMPLE 4

492 g of PFPE from C₃ F₆ (formula IV) having viscosity 1221 c.St. and 10g of AlF₃ phase of type IV, were heated to 360° C. and kept understirring at such temperature for 8 hours.

After filtration of AlF₃, 468 g of PFPE having a viscosity of 403 c.St.and an acidity of 0.2 m.eq.KOH/g of oil were obtained.

EXAMPLE 5

10 g of AlF₃ of type III, obtained by heating type I to 550° for 8hours, were utilized under the same modalities of example 2, but at atemperature of 310° C. for 30 minutes. Starting from 500 g of PFPE ofthe same type as used in example 2, there were obtained 490 g of an oilhaving a viscosity of 246 c.St. and an acidity equal to 0.05 m.e.KOH/gof oil.

EXAMPLE 6

By decomposing (NH₄)₃ AlF₆ at 400° C. in nitrogen, 10 g of AlF₃ type Vwere prepared.

The catalyst so obtained was utilized according to the same modalitiesas example 2, but for a time of 15 minutes, and starting from 500 g ofPFPE of the type used in example 2. 485 g of an oil having a viscosityof 85 c.St. and an acidity equal to 0.17 m.eq.KOH/g of oil wereobtained.

EXAMPLE 7

Into a 4-neck flask of 1 liter capacity, equipped with a stirrer, athermometer, a heated dropping funnel and a heated 50-cm Vigreux columnwith heat without reflux, there were charged 1000 g of PFPE from C₃ F₆(formula IV) having a viscosity of 1382 c.St. and 5 g of AlF₃ of type I;into the dropping funnel there were charged 960 g of the sameperfluoropolyether, which were totally fed in 120 minutes into theflask.

During the reaction there were distilled 1230 g of PFPE having aviscosity of 3.25 c.St. and an acidity of 0.38 m.eq.KOH/g, and therewere collected as a residue, 400 g of a PFPE having a viscosity of 46c.St. in the reactor.

EXAMPLE 8 (degradation of PFPE, Krytox type)

5 g of AlF₃ of type II were added to 500 g of a perfluoropolyetherhaving a viscosity of 990 c.St., obtained by anionic polymerization of##STR9## with CsF, according to U.S. Pat. No. 3,250,808 (Du Pont) andthen neutralized with F₂ at 150° C.

After heating to 300° C. during 120 minutes under stirring, 450 g of aproduct having a viscosity of 175 c.St. and an acidity equal to 0.05m.eq.KOH/g were obtained.

Such product showed interesting structural variations revealed byspectroscopic NMR analysis (carried out at 200 Mc): in particular, withrespect to the starting product, there were observed an increase in thenumber of CF₃ CF₂ CF₂ O-- terminals, a decrease in the number of CF₃ CF₂OCF₂ CF(CF₃)O-- terminals, and the appearance of CF₃ CF₂ OCF(CF₃)CF₂ O--and of (CF₃)₂ CF--O--(CF₃)₂ CFCF₂ -- terminals.

The ratio between the signals of n-propyl terminals and the sum of theethyl terminals is equal to 0.25 in the treated product; while in thestarting material said ratio is comprised between 1 and 1.5.

EXAMPLE 9

1000 g of a perfluoropolyether having a viscosity of 1450 c.St.,obtained by photo-oxidation of perfluoropropene and then reduced andneutralized with F₂, were treated with 1% by weight of AlBr₃ at 180° C.for 20 minutes; 920 g of PFPE having a viscosity of 90 c.St wereobtained.

The product filtered gave 2.9 g of a crystalline substance which,subjected to analysis, resulted to prevailingly consist of AlF₃ type I.

Such product, washed with Freon 113 and dried under vacuum, was added,in the amount of 0.2%, to a PFPE having a viscosity of 1450 c.St, at250° C. under stirring.

After 10 minutes, 70% of the starting PFPE having a viscosity of 30 c.Stwas recovered.

EXAMPLE 10

3000 g of a perfluoropolyether oil from C₃ F₆ (formula IV) having anumeral average molecular weight equal to 6380 a.m.u. were heated in aflask equipped with a refrigerator, a CO₂ trap and a stirrer, up to atemperature of 180° C. Then 15 g of AlBr₃ were added and, maintainingthe mass under stirring, the temperature was brought to 200° C. in atime of 20 minutes. After cooling, the reagent mass was filtered and2800 g of a product having a numeral average molecular weight equal to1480 a.m.u. and an acidity equal to 1.02 m.eq.KOH/g of oil wereobtained. The calculated functionality determined from the MW/EW(molecular weight/equivalent weight) ratio was 0.74.

After neutralization with KOH, the oil was subjected to streamdistillation and 728 g of a neutral product were collected.

The undistillable product showed an acidity equal to 0.67 m.eq.KOH/g ofoil, and a functionality equal to 1.

Almost the same result was obtained by counting the neutral and acidterminals, determinable by means of NMR, then calculating the ratio.

In the dry ice trap there were collected 135 g of a complex mixture ofacid and neutral products having a low average molecular weight, andfurthermore 12 g of bromine.

EXAMPLE 11

By operating as in the Example 10, 26 g of AlBr₃ were added to 3000 g ofperfluoropolyether oil having an average numeral molecular weight equalto 4750 a.m.u.

After filtration, 2580 g of a product having an average numeralmolecular weight equal to 1010 a.m.u. and an acidity of 1.58 m.eq.KOH/gof oil, with a functionality of 0.63 were obtained.

After neutralization with KOH and stream distillation 516 g of a neutralproduct were collected. The distillation residue showed an acidity of0.99 m.eq.KOH/g, and a functionality equal to 1.

210 g of a mixture of acid and neutral perfluoropolyethers and 23 g ofbromine were collected in the dry ice trap.

EXAMPLE 12

A portion of the potassium salt of the PFPE acid obtained in example 11was accurately dried under vacuum at 104° C. for 24 hours. 500 g of theproduct obtained were heated for 4 hours at a temperature of 250° C. Atthe end of the reaction, a weight loss equal to 20.5 g, corresponding tothe formation of about one CO₂ molecule per two molecules of startingproduct, was observed. On I.R. analysis the product showed the typicalband of the vinylether double bond at 1850 cm⁻¹.

EXAMPLE 13

3 g of CoCl₂ (0.3% by weight) were added to 1000 g of aperfluoropolyether obtained by starting from C₃ F₆ and having viscosityof 1400 c.St. The perfluoropolyether containing CoCl₂ was charged in aglass reactor fitted with reflux condenser, stirrer, dry ice trap andtemperature automatic control. The temperature was raised to 220° C. andwas kept at this temperature for 13 hours. During this time gaseousfluorine was continuously introduced at a flow rate of 10 l/hour. Therewere obtained 790 g of neutral perfluoropolyether having viscosity of350 c.St and in the dry ice trap. 109 g of low-boiling products werecollected.

EXAMPLE 14

In the reactor of the preceding example, 1000 g of a perfluoropolyetherof the same type of the preceding example were charged together with 15g of CoCl₂ (1.5% by weight). The temperature was raised at 220° C. andat this temperature the reaction mixture was kept for 13.5 hours, undera flow of gaseous fluorine (flow rate 10 l/hour). 716 g of neutralperfluoropolyether having viscosity 166 c.St. were obtained.

In dry ice trap 147 g of low-boiling compound were collected.

EXAMPLE 15

500 g of PFPE from C₂ F₄ (formula V) having a viscosity of 260 c.St. and5 g of AlF₃ in the α-form (type IV) were placed in a flask equipped witha stirrer, thermometer, a refluxing refrigerator and a CO₂ trap.

The temperature was raised to 250° C. and the reaction mixture was leftat said temperature for 3 hours.

Then the mixture was filtered and 446 g of PFPE having a viscosity of142 c.St. were obtained. In the trap 35 g of PFPE having a viscosity of25 c.St. were recovered.

EXAMPLE 16

Example 15 was repeated but using 10 g of AlF₃.

403 g of PFPE having a viscosity of 65 c.St. were obtained. In the trap42 g of PFPE having a viscosity of 2.3 c.St. were collected.

What is claimed is:
 1. A process for the scission of perfluoropolyethersselected from those having one of the following general formulae:##STR10## in which A is --CF₃ ; --C₂ F₅ ; --C₃ F₇ and Z is A or an acidgroup --COF or a derivative thereof, or the group --CO--CF₃ ;themonomeric units with indexes m, n and r are randomly distributed alongthe chain of the perfluoropolyether, m, n and r are integers from 0 to200, and the value of m+n+r being always greater than zero;

    B--O(--CF.sub.2 CF.sub.2 --O).sub.p --(CF.sub.2).sub.q --Z (II)

in which B is --CF₃, C₂ F₅ ; and Z is B or an acid group --COF or aderivative thereof, the monomeric units with indexes p and q arerandomly distributed along the chain of the perfluoropolyether, p and qare integers and p/q is from 0.5 to 2, extremes included; ##STR11## inwhich Y is an acyl fluoride group --CF(CF₃)COF and m is an integergreater than zero;said process comprising heating the perfluoropolyetherat a temperature from 150° C. to 380° C. in the presence of a catalystcomprising a fluoride and/or oxyfluoride of a metal selected from thegroup consisting of aluminum, titanium, vanadium, cobalt, nickel andmixtures thereof, in amounts corresponding to 0.1% to 2% by weight onthe perfluoropolyether, to obtain the corresponding compounds having alower molecular weight.
 2. The process according to claim 1, in whichthe fluoride and/or oxyfluoride is formed "in situ" by starting fromdifferent compounds of a metal selected from the group consisting of Al,Ti, V, Co, Ni capable of converting to said fluoride and/or oxyfluorideunder the reaction conditions.
 3. The process according to claim 1wherein the catalyst is AlF₃ having a free acidity degree evaluated asirreversibly NH₃ absorbed at 100° C., of at least 2.9 m.eq.KOH/g.
 4. Theprocess according to claim 3, in which the AlF₃ is furthermorecharacterized in that it comprises AlF₃ of the gamma type or of thedelta type or of mixtures thereof.
 5. A process for the scission ofperfluoropolyethers selected from those having one of the followingthree formulae: ##STR12## in which A is --CF₃ ; --C₂ F₅ ; --C₃ F₇ and Zis A or an acid group --COF or a derivative thereof, or the group--CO--CF₃ ;the monomeric units with indexes m, n and r are randomlydistributed along the chain of the perfluoropolyether, m, n and r areintegers from 0 to 200, the value of m+n+r being always greater thanzero;

    B--O(--CF.sub.2 CF.sub.2 --O).sub.p --(CF.sub.2).sub.q --Z (II)

in which B is --CF₃, --C₂ F₅ ; and Z is B or an acid group --COF or aderivative thereof, the monomeric units with indexes p and q beingrandomly distributed along the chain of the perfluoropolyether, p and qare integers and p/q is from 0.5 to 2, extremes included; ##STR13## inwhich Y is the acyl fluoride group --CF(CF₃)COF, and m is an integergreater than zero;said process comprising heating the perfluoropolyetherat a temperature from 150° to 380° C. in the presence of a catalystobtained in situ from CoCl₂ and NiCl₂, in amounts corresponding to 0.1%to 2% by weight based on the perfluoropolyether, and flowing fluorinegas into the reaction mixture.